Project Summary Radiopharmaceutical therapy (RPT) ? the use of targeted radionuclides to deliver radiation specifically to cancer cells and their microenvironment ? is a fundamentally different approach to cancer therapy that is growing, with a substantial number of large and small pharmaceuticals companies developing products in this area and radionuclide producers making substantial investments in scaling up production. This is especially true in the area of alpha emitters. The dosimetric evaluation of therapeutic radiopharmaceuticals is a key requirement for regulatory approval and optimal administration of RPTs, especially in combination with external beam radiation therapy. This project will provide a cloud-based dosimetry software service, delivered through a web-browser, that includes the full complement of methods needed for dosimetry in the context of obtaining regulatory approval of RPTs and, ultimately, for optimal clinical delivery. Providing this in a cloud-based system will enable a variety of models for selling the service that do not require a large up-front capital investment for clinics or radiopharmaceutical developers. It also will provide access to expert advice, customization, and dosimetry services, and allow for collaboration between developers, dosimetry experts, and clinical sites. To accomplish the goal of developing this cloud-based web-browser-delivered RPT dosimetry software service, we propose the following specific aims: (1) Design, develop and implement a web/cloud-based integrated software system for treatment planning of RPT therapy; (2) design and implement a full server-side framework for subscription, authentication, and granting collaborative privileges for the various processes and data in the dosimetry pipeline; (3) optimize and adapt the four most computationally intensive processes for a multi-processor cloud-based compute environment; (4) apply and evaluate the toolchain developed in aims 1-3 to phantom, simulated and existing patient data. Successful completion of this project will produce a cloud-based software system delivered to the user via a web browser that provides an integrated, streamlined, robust, state-of-the-art system for RPT treatment planning. This system would enable a collaborative approach to multi-center clinical trials and eventually to clinical delivery of optimally dosed RPT.